Currently known processes for sulfur dioxide from oxygen-containing gases typically employ caustic processes (see e.g., U.S. Pat. No. 3,719,742 to Terrana et al.; U.S. Pat. No. 3,790,660 to Earl et al.; or U.S. Pat. No. 3,920,794 to La Mantia et al.), or processes that use amine-type solvents to absorb SO2 from a waste gas (see e.g., U.S. Pat. No. 3,904,735 to Atwood et al.) However, several difficulties remain in such processes. Among other things, most caustic processes consume relatively large amounts of energy for stripping and solvent circulation, while many alkanolamines have a relatively low selectivity towards SO2 and tend to absorb significant quantities of CO2.
Alternatively, as described in our International patent application with the serial number PCT/US02/25998 (published as WO 03/045544), sulfur dioxide-containing waste gas is introduced into a reducing gas generator that is operated using natural gas, air, and hydrogen to supply sufficient reducing gas to the effluent gas. Typical operation conditions are selected such that the oxygen is substantially completely removed from the waste gas. The so formed hydrotreated feed gas comprises hydrogen sulfide, which is then removed using a contactor and appropriate solvent. Such configurations advantageously improve sulfur removal under most conditions. However, high temperature operation and supplemental fuel gas are often needed, which tends to increase cost and complexity of the operation. Moreover, such processes often consume significant amounts of energy for solvent circulation and regeneration.
To eliminate problems associated high-temperature operation, configurations may be employed in which sulfur species are removed at moderate temperature (e.g., 600-900° F.) using separate catalytic reactions that take further advantage of the Claus reaction. Exemplary configurations are disclosed in our copending International application with the serial number PCT/US04/12599. Still further alternative configurations that employ catalytic removal of oxygen from the sulfur oxide containing feed gas are described in our copending International application with the serial number PCT/US04/37556. While such configurations are especially advantageous for plants where solvent operation is preferred, various drawbacks may remain. Among other things, such configurations rely at least in part on a Claus-type reaction, which is limited by the relatively unfavorable reaction equilibrium towards sulfur formation. Similarly, as described in U.S. Pat. No. 6,214,311, a Claus process is coupled with direct oxidation of hydrogen sulfide from the upstream Claus reaction to elemental sulfur using a suitable catalyst and excess air. Once more, such configurations often achieve a relatively clean effluent, however, are generally limited by the reaction equilibrium of the Claus reaction.
Thus, although numerous configurations and methods are known in the art to reduce sulfur concentrations in oxygen-containing effluent streams, all or almost all of them suffer from one or more disadvantages. Therefore, there is still a need to provide improved methods and configuration to reduce the sulfur content in such streams.